The present invention relates to industrial process control and monitoring systems. More specifically the present invention relates to field devices in which at least two process variables are sampled for use in monitoring or controlling an industrial process.
Industrial processes are used in the manufacture and refinement of various goods and commodities such as oil, food stuff, pharmaceuticals, paper pulp, etc. In such systems, typically a process variable of a process fluid is measured by a field device. Examples of process variables include pressure, temperature, differential pressure, level, flow rate and others. Based upon this measured process variable, if the industrial process is controlled using a feedback system, the process variable can be used to adjust or otherwise control operation of the industrial process.
Some types of process variables are measured or calculated based upon measurement of two, or more, other process variables. For example, a differential pressure can be measured by measuring two separate process fluid pressures and subtracting the two measurements. The differential pressure can be used in determining flow rate or level of process fluid in a container.
However, when using two separate process variables to determine a third process variable, errors due to time skew error can be introduced into the determination.